The overall objective of this research is to determine if exposure to ultrasound hyperthermia can enhance the effects of x-irradiation on tumors and normal tissues. Ultrasound was capable of reducing the TCD50 (the radiation dose required to cure 50 percent of the tumors) for some, but not all of the transplantable tumors tested. Ultrasound levels of 1.5 W/sq. # cm (1.9 MHz, C.W.) for 15 minutes produced marked reductions in growth in treated bone and paralysis after spinal cord treatment. Combined studies (x-ray and ultrasound) are underway.